The ultimate objective of our present research is to clarify the function of plasma lipoproteins in atherosclerosis. We are focusing on the various physicochemical and enzymatic factors which account for the retention and accumulation of plasma lipoproteins in the aorta. We are attempting, by the use of model systems, to clarify the alterations in the surface and interior properties of the lipoproteins which take place during their circulation and following their entry into the aorta. We are also examining the interactions of these lipoproteins with connective tissue components in the aorta, including elastin, acid mucopolysaccharide, and collagen. Concerning changes occurring in lipoproteins during circulation, we are concentrating on lecithin-cholesterol acyltransferase and lipoprotein lipase. We will determine the effects of proteolytic, lysosomal, and other enzymes on modifications of lipoproteins following their entry into the aorta. In our research, we intend to use both swine and human plasma lipoproteins; swine aortic tissue will serve as a source of various enzymes and of connective tissue components. We are hoping to demonstrate that the accumulation of lipids in atherosclerosis is caused by changes in the physical state of lipoproteins and lipids and in their macro- and microenvironments.